1. Field of the Invention
This invention relates to a device for connecting a wheel or wheel-like body to a shaft, and more particularly to a device which can rigidly connect a body to a shaft at any axial and rotational position on the shaft with a high accuracy of centering. The body and shaft are connected by tightening a nut, and the body is positively disconnected from the shaft when the nut is loosened.
2. Description of the Prior Art
A known device for connecting a wheel to a shaft is shown in FIG. 1. The wheel 2, for example a gear, has a hub 3. The hub 3 has an axial bore through which a rotary shaft 1 extends. The prior art device includes an inner ring 5 fitted about the shaft 1. The bore in the hub has an enlarged diameter portion 4 in which the inner ring 5 is fitted. The inner ring 5 has a slit 6 extending along its entire length, allowing it to expand and contract in circumference. The inner ring 5 has an outer periphery with a tapered portion 7 located within the enlarged diameter portion 4 of the hub and a threaded portion 8 located outwardly of the hub. The device also includes an outer ring 10 having an axial slit 9. The outer ring 10 is fitted in the enlarged diameter portion 4 and has a tapered inner peripheral surface 11 which is complementary to the tapered portion 7 of the inner ring 5. A lock washer 12 is positioned in contact with the outward end of the outer ring 10 and has an inner edge projection 13 engaged in the slit 6. A nut 14 is threadedly engaged about the threaded portion 8 of the inner ring 5. An opposing wedge action is developed by the tapered surfaces 7 and 11 when the nut 14 is tightened. The relative axial displacement of the inner and outer rings 5 and 10 forces into intimate contact with the shaft 1 and the peripheral wall of the enlarged diameter portion 4 of the bore in the wheel 2, respectively, whereby the wheel 2 is secured to the shaft 1. The washer 12 also has an outer edge projection folded over the nut 14.
The prior art device does not include any mechanism enabling forced disengagement of the rings 5 and 10. It is, therefore, necessary that the tapered surfaces 7 and 11 have a sufficiently large taper angle to inherently urge the outer ring 10 outwardly along the shaft, thereby to release its wedge action when the nut 14 is loosened.
As a matter of geometry, the wedge taper results in a definite relationship between axial displacement of the wedge rings and the resulting radial displacement or force. Rotation of nut 14 forces axial displacement of rings 5 and 10 in an amount determined by the pitch of the thread. The axial displacement of rings 5 and 10 results in a corresponding radial displacement of outer ring 10 in an amount determined by the tangent of the taper angle. The pitch and taper angle also determine the degree of force exerted radially as a result of a given torque on the nut, in the same way. For purposes of illustration, the prior art device shown in FIG. 1 has a taper angle of about 16 degrees. The device of the invention as illustrated in FIGS. 2-4 has a taper angle, for example, of less than 1/5 that of the device of FIG. 1, about three degrees.
The relatively large taper angle needed to release wedge ring 10 has a number of disadvantages. Firstly, the device fails to produce a sufficiently large force for securing the wheel to the shaft, because the available torque for tightening nut 14 is opposed by the steeply-tapered surfaces 7, 11. Secondly, as a result of the steep taper angle, each of the inner and outer rings 5 and 10 have a relatively short axial length. Inasmuch as the wheel 2 is ultimately supported along the short axial length of the taper rings, it is not possible to dependably achieve and hold a high accuracy of centering for the wheel 2 relative to the shaft 1. As a result, the wheel 2 must frequently be provided with an additional centering guide surface 15, spaced from the wedge structure and functioning like an outrigger to limit the centering error. Thirdly, the washer 12 or like means is essential for locking the nut 14 in its tightened position against the force of the steeply-tapered wedges so that the nut cannot be loosened by vibration.